EICR classification codes describe the significance of observations recorded during periodic inspection and testing of an existing electrical installation. C1 means danger is present, C2 means potentially dangerous, C3 means improvement is recommended and FI identifies a matter requiring further investigation. They should not all be described as “failure codes”.
The important 2026 change concerns FI.
BS 7671:2018+A4:2026 expressly separates C1 and C2 from the advisory C3 and FI classifications. Under the Amendment 4 model EICR, C1 or C2 affects the overall assessment and results in an unsatisfactory report, while C3 and FI do not by themselves affect the overall assessment. FI wording has also changed to “further investigation is advised”.
EICR Classification Codes at a Glance
Classification codes communicate the significance and urgency of individual observations. The code should reflect the condition actually identified during inspection and testing, rather than simply whether an installation differs from the latest edition of BS 7671.
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The
IET Amendment 4 model EICR
now makes this distinction explicit: C1 and C2 affect the overall assessment, while C3 and FI are advisory.
This article does not rank EICR faults by frequency.
No RCD Electrical inspection dataset has been supplied for this page, so it does not claim that a particular defect is the most common reason for EICR problems in London, nor does it make statistical claims about Victorian, Edwardian or other property types.
Which Codes Make an EICR Unsatisfactory Under Amendment 4?
Under BS 7671:2018+A4:2026, C1 and C2 are the classifications that affect the overall assessment and result in an unsatisfactory EICR. C3 and FI are shown separately as advisory observations and do not affect the overall assessment by themselves.
This distinction is important because the phrase “failed EICR codes” can be misleading. C3 has never meant that danger is present, and the Amendment 4 model now expressly confirms that FI should not automatically be treated as an unsatisfactory outcome.
What Does C1 Mean on an EICR?
C1 means danger is present.
The inspector has identified a condition where there is a risk of injury and immediate remedial action is necessary. A C1 observation affects the overall assessment and results in an unsatisfactory EICR.
C1 should reflect an actual dangerous condition identified during the inspection. It should not be used merely because equipment is old, because an installation was designed to an earlier edition of the Wiring Regulations, or because an improvement could be made.
What Does C2 Mean on an EICR?
C2 means potentially dangerous.
The condition does not necessarily present the immediate risk associated with C1, but it is considered capable of giving rise to danger and requires urgent remedial action. A C2 observation results in an unsatisfactory overall assessment.
The classification depends on the actual electrical condition, the protective measures present and the risk created by the defect. Code selection therefore requires engineering judgement rather than a simple age-based or component-based checklist.
Does C3 Mean an EICR Has Failed?
No. C3 means improvement recommended.
It is advisory and does not by itself make the EICR unsatisfactory.
An existing installation may differ from current BS 7671 requirements without automatically being dangerous. The IET explains that standards are not retrospective: an installation complying with an earlier edition is not necessarily unsafe simply because the current standard has changed.
A C3 observation allows the inspector to recommend an improvement where appropriate without incorrectly describing the existing condition as dangerous or potentially dangerous.
What Does FI Mean on an EICR?
FI means that further investigation is appropriate because a potential safety issue could not be fully determined within the extent or limitations of the periodic inspection.
Under Amendment 4:2026, the wording is “further investigation is advised”.
The FI classification should not be used simply because additional diagnostic work would be convenient. Periodic inspection and testing is intended to assess the condition of the installation; it is not a general fault-finding exercise.
For example, if inspection or testing has already identified a definite defect or non-compliance capable of being classified, the observation should receive the appropriate classification. Investigation needed later to find the precise cause of that established defect can be separate fault-finding work rather than a reason to use FI automatically.
The wider inspection boundary is explained separately in
What Does EICR Check Include UK?.
That article owns the detailed question of what the EICR inspects and tests; this page owns the meaning and effect of the resulting classification codes.
BS 7671 Amendment 4:2026 and the FI Transition
BS 7671:2018+A4:2026 was published on 15 April 2026. The IET states that the previous Amendment 2 / Amendment 3 position remains available during a six-month transition and is withdrawn on 15 October 2026, after which Amendment 4 must be used.
The transition matters because FI wording has changed. Earlier EICR material used the wording “further investigation required without delay”. Amendment 4 changes this to “further investigation is advised” and expressly separates FI from the C1 and C2 classifications that affect the overall assessment.
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During the transition, it is therefore inaccurate to state simply that “FI always fails an EICR” or, without context, that every historical FI observation should be interpreted using the new Amendment 4 wording. Check the standard stated on the actual report and read the inspector's overall assessment.
Does Every BS 7671 Non-Compliance Need a C1 or C2 Code?
No.
An EICR is an assessment of the condition and safety of an existing installation, not a retrospective exercise requiring every older installation to be upgraded automatically to the latest edition of BS 7671.
The IET states that standards are not retrospective. An installation designed and installed to an earlier edition is not necessarily unsafe merely because requirements have since changed. The inspector must consider the actual condition and apply the appropriate classification using engineering judgement.
This is one reason C3 exists: an improvement can be recommended without concluding that the condition is dangerous or potentially dangerous.
What Do C1, C2, C3 and FI Mean for Landlords in England?
The EICR classification system and landlord legislation need to be read together but should not be treated as the same thing.
Current
GOV.UK electrical safety guidance for landlords
still uses the earlier FI wording “further investigation required without delay”. It also states that C1 or C2 makes the installation unsatisfactory and that where the report shows remedial or further investigative work is necessary, the landlord must complete that work within 28 days or within any shorter period specified in the report.
This creates an important 2026 distinction.
The current GOV.UK guidance has not simply been rewritten around the new Amendment 4 FI wording. Amendment 4 says FI is advisory and does not affect the overall EICR assessment by itself; landlord duties, however, still require action where the actual report says further investigative work is necessary. Landlords should therefore follow the report they have received rather than treating “FI” in isolation as either an automatic failure or something that can automatically be ignored.
The five-year inspection requirement, report-copy deadlines, 28-day remedial-work rule and 2026 social-housing transition are owned by
London Rental Electrical Safety in 2026: What Landlords Need to Know About EICR Compliance.
What Should You Do After Receiving an EICR with Classification Codes?
Start with the exact observation and the overall assessment, not just the classification letters. The code communicates the significance of the observation, while the wording of the report identifies what was found and what action or investigation is appropriate.
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Check which circuit or part of the installation is affected.
A code should be tied to a specific observation rather than interpreted in isolation.
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Check the overall assessment.
Under Amendment 4, C1 and C2 affect the satisfactory or unsatisfactory outcome; C3 and FI are advisory.
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Check which BS 7671 amendment the report uses.
This is particularly important for FI during the 2026 transition.
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Distinguish remedial work from further diagnosis.
Some observations already identify the defect. Others may justify additional investigation.
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Do not assume the whole property needs rewiring.
The required response should follow the actual observation and its extent.
If the report has identified a particular electrical problem that then needs diagnosis, targeted
electrical fault finding
can be a separate next step.
References & Standards
These sources support the current classification-code, FI-transition and landlord-compliance information used in this guide.
Need Help Understanding an EICR?
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